The present invention relates to the external sealing and joining of piping. More particularly, the invention provides an improved seal profile which is suitable for use inside pipe couplings.
A pipe coupling may be sealed by means of a pair of discrete seals proximate to each of the opposed axial faces of the coupling. Improved stability is however obtained when a single twin-lip seal is used. The wider seal costs somewhat more than a pair of short seals, but the added stability outweighs the added cost. Seals of both types are in common use. The profile of a typical prior art, two-lipped coupling seal will be described with reference to FIG. 1.
While the prior-art two-lipped coupling seals as described have served well in many applications, under some conditions, for example when a pipe being clamped moves axially outwards and/or when heavy pressure has been applied to the seal, it has been found that the seal lip moves axially outwards away from the pipe joint. Such undesired movement is encouraged by the slope of the outer face of the support block. This causes loss of sealing pressure and if continued leads to leakage of the fluid being transported in the pipeline.